1. Field of the Disclosure
This disclosure relates to an optical code reader system. In particular, this disclosure relates to an optical code reader system and method for control of illumination for aiming and exposure.
2. Description of the Related Art
Optical codes are patterns made up of image areas having different light reflective or light emissive properties, which are typically assembled in accordance with a priori rules. The term “barcode” is sometimes used to describe certain kinds of optical codes. The optical properties and patterns of optical codes are selected to distinguish them in appearance from the background environments in which they are used. Devices for identifying or extracting data from optical codes are sometimes referred to as “optical code readers” of which barcode scanners are one type.
Optical code readers are used in either fixed or portable installations in many diverse environments such as in stores for check-out services, in manufacturing locations for work flow and inventory control and in transport vehicles for tracking package handling. The optical code can be used as a rapid, generalized means of data entry, for example, for reading of a target barcode from a printed listing of many barcodes. In some uses, the optical code reader is connected to a portable data processing device or a data collection and transmission device. Frequently, the optical code reader includes a handheld sensor which is manually directed at a target code.
An example of a conventional optical code is a one-dimensional barcode symbol. The barcode is a pattern of variable-width rectangular bars separated by fixed or variable width spaces. The bars and spaces have different light reflecting characteristics. One example of a one dimensional barcode is the UPC/EAN code used to identify, for example, product inventory. An example of a two-dimensional or stacked barcode is the PDF417 barcode. A description of PDF417 barcode and techniques for decoding it are disclosed in U.S. Pat. No. 5,635,697 to Shellhammer et al., and assigned to Symbol Technologies, Inc., which is incorporated herein by reference in its entirety. Another conventional optical code is known as “MaxiCode”. It consists of a central finder pattern or bull's eye center and a grid of hexagons surrounding the central finder. It should be noted that the aspects of the disclosure are applicable to optical code readers in general, without regard to the particular type of optical codes which they are adapted to read. The disclosure described may also be applicable to some associated image recognition or analysis.
Optical code readers may be laser-based or imager-based. In a conventional imager-based optical code reader an imaging engine is provided having an image sensor having a two-dimensional array of cells or photo sensors, such as an area charge coupled device (CCD), which correspond to image elements or pixels in a field of view of the engine. The imaging engine further includes a lens assembly for focusing light incident on the image sensor and associated circuitry coupled to the image sensor outputting an array of electronic signals corresponding to a two-dimensional array of pixel information for the field of view. The electrical signals are digitized and provided as image data to a processor for processing thereof, including processing the image data for decoding the optical code.
An imager-based optical code reader typically further includes an aim assembly and/or an illumination assembly. Depending on the design of the optical code reader, upon a trigger pull a scan cycle is initiated, beginning with an aim period, during which the operator has an opportunity to aim the optical code reader at the target. During the aim period the aim assembly produces a visible aim pattern, such as a cross-hair or marker indicating the borders of the field-of-view, which is projected from the optical code reader as the reader is aimed at a target to assist the operator in aiming at the desired target. At the end of the aim period an exposure period is provided during which internal illumination is provided by the illumination assembly, and the array of photo sensors sense incident light. Depending on the design, projection of the aim pattern may be disabled during the exposure period, particularly when the aim pattern interferes during exposure.
The exposure period is followed by a decode period is provided, during which the sensing signals corresponding to the sensing during the exposure period are processed by at least one processing device, including for attempting to perform a decode operation. The decode period may be followed by another at least one period, such as a data transmission/ period, during which decoded data is transmitted to a another processing device, e.g., a host processor; and/or a status indicator period, during which an audio or visual indication is provided to the user indicating that a decode has occurred. In accordance with the design for some optical code readers, several scan cycles are repeated until the occurrence of an event, such as a successful decode operation is performed, a time out condition occurs or the trigger is released.
Prior art linear imager-based optical code readers may include a dual aim/illumination assembly having a light source which generates a light that is focused into a relatively narrow line. The narrow line of illumination provides two functions, where the first function includes providing a visible light pattern that the user can see and use for aiming the reader by placing the visible narrow line of illumination on the target optical code, and illuminating the linear field of view of the reader, so that when the reader is properly aimed, the target optical code is illuminated by the narrow line and the reader can decode the target optical code.
A read operation may include a series of exposure periods. During an exposure period an image of the target optical code is acquired. Motion of the reader or the target optical code during image acquisition can cause the image to be smeared and render it undecodeable. Accordingly, the exposure period is minimized for decreasing sensitivity to motion. Sufficient illumination is required for image acquisition. However, the shorter the short exposure period, the brighter the illumination for acquiring the image must be. In between exposure periods an image is not acquired, and the target optical code does not need to be illuminated for the purpose of acquiring an image. However, the aiming pattern is typically provided by the illumination system in between the exposure periods for easing aiming of the reader.
When the illumination intensity is increased for the purpose of minimizing sensitivity to motion, the reader requires an increased amount of current to the light source. When the current provided to the illumination system is increased for reducing motion sensitivity during the exposure periods, the same increased current is provided in between the exposure periods for generation of the aiming pattern, although there is not a need for increasing the intensity of the aiming pattern. The current requirements may exceed the output of an available power supply or consume a battery power supply exceedingly fast.
Accordingly, it is an aspect of the present disclosure to provide a system and method which decreases power consumption by a dual aim/illumination assembly of an optical code reader, while minimizing the exposure period for decreasing sensitivity to motion.